The interaction between mast cells and eosinophils is important in the pathogenesis of allergic diseases such as asthma and in the host response against certain pathogens and tumor cells. The generation of reactive oxygen species [e.g. oxidants produced by the eosinophil peroxidase (EPO)-hydrogen peroxide (H202)-halide system] and 5-lipoxygenase (LO) pathway arachidonic acid metabolites [e.g. , leukotriene (LT)s B4, C4, and D4] is critical to the inflammatory function of these cells. Specific aim la) is to study the expression of the 5-LO pathway in the development and maturation of mast cells. We will examine at what stage of mast cell maturation does IgE-mediated signal transduction lead to eicosanoid release in IL-3-dependent mouse bone marrow cultured mast cells. We will examine transcription of mRNA coding for key proteins [i.e., 5-LO, 5-LO activating protein (FLAP), leukotriene A4 hydrolase (LTA4H)] required for leukotriene formation. Specific aim 1b) is to study the effect of specific inhibitors of the 5-LO pathway on degranulation of connective tissue and mucosal mast cells in vitro and in vivo. Specific aim 2 is to study the expression of 5-LO pathway components in a) cytokine (i.e., IL-3, IL-5, GM-CSF)-activated eosinophils in vitro and b) mast cells and eosinophils in late-phase allergic skin responses in vivo. Specific aim 3a) is to study the cytotoxic effect of eosinophils and mast cells singly or in combination on human immunodeficiency virus (HIV)-l. We have observed that mast cells, like eosinophils, exert potent dytotoxicity activity against the AIDS pathogen Toxoplasma gondii. Specific aim 3b) is to study the role of epsilon-BP, a beta-galactoside-binding lectin with affinity for IgE, in mast cell- and eosinophil-mediated killing of T. gondii tachyzoites in vitro. The goal of these studies is to further define the role of mast cells and eosinophil interaction in the pathogenesis of allergic diseases and host defense against pathogens.